1. Field of the Invention
The present invention relates to a process for reducing or retarding the amount of gram negative bacteria for specific classes of food products by treatment with gram positive bactericidal compounds. More specifically, the process comprises first applying one or more highly alkaline substances to the food surface to be treated to disrupt the structure of the outer membrane of the gram negative bacteria followed by treatment with a gram positive bactericide.
2. Technology Description
There has been extensive research conducted in the field of food safety to develop compositions which function as food grade anti-bacterials. In particular, gram negative bacteria such as E. Coli, salmonella, campylobacter and the like pose significant risk to consumers of food. Also, gram negative spoilage bacteria such as pseudomonas, alcaligenes, and erwinia species can cause spoilage, though not illness, and are often the principal factors in reducing the shelf life and freshness of selected processed foods. Both pathogenic and spoilage bacteria occur primarily at the surfaces of food which come into contact with the bacteria by contamination environmental sources. The bacteria can then spread to other parts of the food through mixing, comminuting, or other direct contact. These bacteria then grow during handling and storage of the food, resulting in either spoilage or a pathogenic risk in the food.
Largely because of the strong consumer desire for convenience foods, there has been a wide increase in certain products such as cut vegetables, cut fruits, and the like. The so-called "salad in a bag" products have gained great consumer acceptance as a result of their convenience of use. However, such products are much more susceptible to bacterial degradation as a result of cross contamination with gram negative bacteria occurring at the surface of one or more cut pieces of vegetables contacting other cut pieces present in the package.
In addition there continues to be great concern over the possible contamination of ground meat and seafood as a result of gram negative bacteria. Such contamination has caused deaths and product recalls, closing of plants due to sanitary concerns, and the like. Much of the pathogenic concern associated with these foods is caused by gram negative bacteria such as E. coli H7:0157 and Campylobacter jejuni.
U.S. Pat. Nos. 5,096,718 and 5,260,061 disclose the use of metabolites of propionic acid bacteria in certain foods to increase the shelf life of the resulting products. These metabolites demonstrate enhanced efficacy against gram negative bacteria but are not as effective against gram positive bacteria.
JP 07-115950 suggests the combination of bacteriocins produced by lactic acid bacteria of the propionibacterial genus in combination with either organic acids and their salts, fatty acid esters of polyhydric alcohols, amino acids, antibacterial peptides and proteins, polysaccharides comprising sugars, saccharic acids and amino sugars and their partial decomposition products, spices and their essential oils and plant components; and alcohols.
U.S. Pat. No. 5,217,250 suggests the use of nisin compositions as bactericides. Nisin is a lantibiotic, more specifically, a polypeptide with antimicrobial properties which is produced in nature by various strains of the bacterium Streptococcus lactis. Nisin is primarily effective against gram positive bacteria. This patent suggests that the combination of a chelating agent, such as EDTA or other acetate salts or citrate salts with nisin can result in a broad range bactericide.
U.S. Pat. Nos. 5,573,797; 5,593,800 and 5,573,801 disclose antibacterial compositions which include a combination of a Streptococcus or Pediococcus derived bacteriocin or synthetic equivalent antibacterial agent in combination with a chelating agent. The composition is applied to the surface of the food to be treated either by direct application or by incorporating the composition onto a flexible film casing which is placed into intimate contact with the food surface. The chelating agent binds free divalent cations in the outer membrane of gram negative cells, improving permeability to the antibacterial agents.
U.S. Pat. No. 5,458,876 suggests the combination of a antibiotic with lysozyme as an antibacterial. In this case, lysozyme breaks down the cell wall and weakens the structural integrity of the target cell so that the antibacterial agent becomes more effective in damaging or killing the bacterial cell.
EP 0 466 244 discloses a composition having improved antibacterial properties comprises a mixture of at least one of each of the following groups of compounds: (I) a cell wall lysing substance or a salt thereof, (II) an antibacterial compound and (III) an adjuvant selected from organic acids acceptable for use in food products or preparations for cosmetic use or personal hygiene or salts of these acids, phosphates and condensed phosphates or the corresponding acids, and other sequestering agents. Preferably (I) is lysozyme, (II) may be a bacteriocin (e.g. nisin or pediocin), and (III) may be acetic acid, lactic acid, citric acid, propionic acid, tartaric acid, orthophosphates, hexametaphosphates, tripolyphosphates, other polyphosphates or sequestering agents containing substituted or non-substituted amino groups, for example EDTA.
EP 0 453 860 suggests the combination of nisin with a phosphate buffer effective at a pH of between 5.5 and 6.5 to eradicate gram negative bacteria from surfaces.
WO 97/23136 suggests a bacterial decontamination method which involves treatment with a solution of low concentration alkali metal orthophosphate combined with either osmotic shock and/or lysozyme in solution and/or nisin in solution. This reference tested the combination of low concentrations of trisodium orthophosphate with lysozyme against certain bacteria on lettuce leaves or chicken skin, and the combination of low concentrations of trisodium orthophosphate with nisin against certain bacteria on chicken skin.
Published Australian patent application AU-A-18604/88 discloses the use of bacterialyzing enzyme products with N-acetylmuramidase, e.g. lysozyme, together with non-enzymatic preservatives for preserving foodstuffs. Non-enzymatic preservatives mentioned in this publication are complexing agents such as citric acid and EDTA, amino acids, particularly proteinogenic acids, such as cysteine, alanine, tyrosine and glycine and nucleosides and nucleotides such as inosine 5'-inosine monophosphate or phosphates such as tetrasodiumpyrophosphate (diphosphate), sodium tripolyphosphate (triphosphate) and polyphosphate or reddening agents such as alkali metal nitrates.
Despite the above teachings, there still exists a need in the art for a method for treating food surfaces, and specifically cut vegetables, cut fruits, ground meat or seafood, which is effective against gram negative bacteria. More specifically, there exists a need for more effective treatments that can be readily integrated into existing processing protocols for these products.